Circuit arrangement which cools charging air and method for the operation of said type of circuit arrangement

ABSTRACT

The invention relates to a circuit arrangement ( 1 ) comprising a low temperature circuit ( 2 ) in order to cool charging air in a motor vehicle, comprising a turbo charger and motor cooling circuit ( 3 ) which cools a motor ( 4 ). The low temperature circuit ( 2 ) can be temporarily coupled to the motor cooling circuit ( 3 ) in such a manner that the coolant can pass from one circuit ( 2, 3 ) to another ( 2, 3 ) and back again. The invention also relates to a method the operation of said type of circuit arrangement ( 1 ).

The invention relates to a circuit arrangement which cools charging airin a motor vehicle comprising a turbocharger, according to the preambleof claim 1, and to a method for the operation of said type of circuitarrangement, according to the preamble of claim 6 or 7.

According to the prior art, to increase the power of engines,turbochargers are used in order to compress the air. In this case,however, a heating of the air, designated below as charging air, totemperatures above 100° C. occurs because of compression in theturbocharger. In order to reduce such air heating, air coolers are usedwhich are arranged in the front in the cooling module and serve forcooling the charging air. The charging air in this case flows through aheat exchanger, through which ambient air flows and which isconsequently cooled. It is thereby possible to cool the charging air toa temperature which is about 15-50 K above the temperature of theambient air.

Furthermore, it is known that the cooling of the charging air takesplace via a refrigerant circuit, for example a low temperature circuitin which the refrigerant is cooled to very low temperatures. By means ofthis cold refrigerant, the charging air is cooled down to apredetermined cooling temperature in a charging-air/coolant cooler. Forthe connection of the low temperature circuit, there are two variants,to be precise an integration of the low temperature circuit into asecondary circuit of the engine cooling system or a design in the formof a separate circuit.

The design as a separate circuit has the advantage that low temperaturescan be achieved.

Where the integrated circuit is concerned, an additional pump may bedispensed with if there is appropriate connection. However, there iscoupling to the temperature of the main circuit by means of the enginethermostat, so that, in the case of a high outside temperature or inpart load operation, the same cooling cannot be achieved as in the caseof a separate circuit. Moreover, as regards outlet regulation, that isto say the thermostat is arranged at the engine outlet, the lowtemperature circuit has to be mounted on the pump pressure side. Thisincreases the pressure in the low temperature cooler, which may lead toproblems with regard to fatigue strength.

The object of the invention is to improve a circuit arrangement of thetype initially mentioned.

This object is achieved by means of a circuit arrangement having thefeatures of claim 1.

According to the invention, a circuit arrangement with a low temperaturecircuit for the cooling of charging air in a motor vehicle comprising aturbocharger and an engine cooling circuit for cooling an engine isprovided, the low temperature circuit being capable of being temporarilycoupled to the engine cooling circuit in such a way that coolant canpass from one circuit into the other circuit and back, with the resultthat the advantages of a separate arrangement of the low temperaturecircuit and engine cooling circuit and of a permanently interconnectedarrangement of the low temperature circuit and engine cooling circuitare combined.

Preferably, a feedline is provided between the engine cooling circuitand the low temperature circuit. By means of the feed line, which leadspreferably from an engine thermostat, arranged in the engine coolingcircuit downstream of the engine, as seen in the flow direction, to amixed thermostat integrated into the low temperature circuit, warmcoolant can pass from the engine cooling circuit into the lowtemperature circuit.

For the return of coolant out of the low temperature circuit into theengine cooling circuit, a feedback line is preferably arranged betweenthe mixed thermostat and the engine thermostat.

The mixed thermostat is preferably an expansion thermostat or anelectrically or pneumatically actuable valve.

To operate the circuit arrangement, coolant flows out of the enginecooling circuit into the low temperature circuit preferably during thewarm-up of the engine. This serves for accelerating the warm-up.

In the warm state of the engine, that is to say in normal operation,preferably warm coolant can flow out of the engine cooling circuit intothe low temperature circuit in order to assist the regeneration ofparticle filters. Warm coolant from the engine cooling circuit thusheats charging air in the charging-air/coolant cooler. Furthermore, thecooling of the charging air may be limited in order to prevent theengine from cooling down under specific ambient conditions.

The separation of the two circuits during normal operation leads to ahigh cooling of the charging air and consequently to a high engine powerand to low NO_(x) fractions in the exhaust gas.

The invention is explained in detail below by means of an exemplaryembodiment, with reference to the drawing.

The single FIGURE of the drawing shows a circuit arrangement 1 with alow temperature circuit 2 for the cooling of charging air and with anengine cooling circuit 3 (main circuit) for cooling an internalcombustion engine, designated below as the engine 4.

The engine cooling circuit 3 comprises the engine 4, an enginethermostat 5, a coolant cooler 6 and a coolant pump 7. A feedline 8, thefunction of which is described in more detail at a later juncture, isprovided from the mixed thermostat 5 to the low temperature circuit 2. Abypass 9 is provided between the engine thermostat 5 and the linebetween the coolant cooler 6 and coolant pump 7, so that coolant can beled past the coolant cooler 6.

The low temperature circuit 2 comprises a coolant pump 10, a mixedthermostat 11, in the present case an expansion thermostat, acharging-air/coolant cooler 12 and a low temperature cooler 13. Theabovementioned feedline 8 issues into the mixed thermostat 11.Furthermore, a feedback line 14 is provided between the line downstreamof the mixed thermostat 11 and upstream of the low temperature cooler 13and downstream of the coolant cooler 6 and upstream of the coolant pump8.

An air conveying device, indicated diagrammatically on the right of thecoolant cooler 6 in the figure, with one or more sucking and/ordelivering fans supplies the coolant cooler 6 and the low temperaturecooler 13 with cooling air, the cooling air flowing first through thelow temperature cooler 13 and subsequently through the coolant cooler 6.

The circuit arrangement 1 functions as follows. In a normal operatingstate, the coolant of the low temperature circuit 2 is heated relativelysharply when it flows through the charging-air/coolant cooler 12. Inthis case, the mixed thermostat 11 is closed with respect to thefeedline 8, so that no coolant can pass from the engine cooling circuit3 into the low temperature circuit 2, and there are two separatecircuits, as is known from the prior art.

During the warm-up of the engine 4 or under other operating conditionsin which the charging-air cooling has to be limited or the charging aireven has to be heated up, the coolant leaves the charging-air/coolantcooler 12 at a relatively low temperature. In these situations, themixed thermostat 11 opens with respect to the feedline 8, so thatcoolant can flow out of the engine coolant circuit 3 into the lowtemperature circuit 2. The coolant from the engine cooling circuit is,if appropriate, mixed in the mixed thermostat 11 with cold coolant fromthe low temperature circuit 2, which flows into the mixed thermostat 11from the coolant pump 10, and is supplied to the charging-air/coolantcooler 12. The supply of coolant out of the engine cooling circuit 3into the low temperature circuit 2 is compensated by means of acorresponding backflow of coolant out of the low temperature circuit 2into the engine cooling circuit 3 via the feedback line 14.

In order to make it possible, out of normal operation, to heat up thecharging air in regeneration phases of particle filters, the mixedthermostat 11 is opened with respect to the feedline 8, although thecoolant leaves the charging-air/coolant cooler 12 in a relatively highlyheated estate. In this case, electrically heating is provided in themixed thermostat 11 designed as an expansion thermostat, heating takingplace during normal operation. Switching off the heating by means of theengine electronics then leads to a corresponding influence being exertedon the expansion thermostat.

If a valve actuated by external energy is provided instead of anexpansion thermostat, then, if required, external energy is activated asa result of a control signal.

List of Reference Symbols

-   1 Circuit arrangement-   2 Low temperature circuit-   3 Engine cooling circuit-   4 Engine-   5 Engine thermostat-   6 Coolant cooler-   7 Coolant pump-   8 Feedline-   9 Bypass-   10 Coolant pump-   11 Mixed thermostat-   12 Charging-air/coolant cooler-   13 Low temperature cooler-   14 Feedback line

1. A circuit arrangement with a low temperature circuit for the coolingof charging air in a motor vehicle comprising a turbocharger and anengine cooling circuit for cooling an engine, wherein the lowtemperature circuit can be temporarily coupled to the engine coolingcircuit in such a way that coolant can pass from one circuit into theother circuit and back.
 2. The circuit arrangement as claimed in claim1, wherein a feedline between the engine cooling circuit (3) and the lowtemperature circuit is provided.
 3. The circuit arrangement as claimedin claim 2, wherein the feedline leads from an engine thermostat,arranged in the engine cooling circuit downstream of the engine, as seenin the flow direction, to a mixed thermostat integrated into the lowtemperature circuit.
 4. The circuit arrangement as claimed in claim 3,wherein a feedback line is arranged between the mixed thermostat and theengine thermostat.
 5. The circuit arrangement as claimed in claim 2,wherein the mixed thermostat is an expansion thermostat or anelectrically or pneumatically actuable valve.
 6. A method for operatinga circuit arrangement as claimed in claim 1, wherein, during the warm-upof the engine, coolant flows out of the engine cooling circuit into thelow temperature circuit.
 7. A method for operating a circuit arrangementas claimed in claim 1, wherein, in the warm state of the engine, coolantflows out of the engine cooling circuit into the low temperaturecircuit.
 8. The method as claimed in claim 6, wherein warm coolant fromthe engine cooling circuit (3) is used for the heating of charging airin the charging-air/coolant cooler (12).
 9. The circuit arrangement asclaimed in claim 3, wherein the mixed thermostat is an expansionthermostat or an electrically or pneumatically actuable valve.
 10. Thecircuit arrangement as claimed in claim 4, wherein the mixed thermostatis an expansion thermostat or an electrically or pneumatically actuablevalve.
 11. A method for operating a circuit arrangement as claimed inclaim 2, wherein, during the warm-up of the engine, coolant flows out ofthe engine cooling circuit into the low temperature circuit.
 12. Amethod for operating a circuit arrangement as claimed in claim 3,wherein, during the warm-up of the engine, coolant flows out of theengine cooling circuit into the low temperature circuit.
 13. A methodfor operating a circuit arrangement as claimed in claim 4, wherein,during the warm-up of the engine, coolant flows out of the enginecooling circuit into the low temperature circuit.
 14. A method foroperating a circuit arrangement as claimed in claim 5, wherein, duringthe warm-up of the engine, coolant flows out of the engine coolingcircuit into the low temperature circuit.
 15. A method for operating acircuit arrangement as claimed in claim 2, wherein, in the warm state ofthe engine, coolant flows out of the engine cooling circuit into the lowtemperature circuit.
 16. A method for operating a circuit arrangement asclaimed in claim 3, wherein, in the warm state of the engine, coolantflows out of the engine cooling circuit into the low temperaturecircuit.
 17. A method for operating a circuit arrangement as claimed inclaim 4, wherein, in the warm state of the engine, coolant flows out ofthe engine cooling circuit into the low temperature circuit.
 18. Amethod for operating a circuit arrangement as claimed in claim 5,wherein, in the warm state of the engine, coolant flows out of theengine cooling circuit into the low temperature circuit.
 19. A methodfor operating a circuit arrangement as claimed in claim 6, wherein, inthe warm state of the engine, coolant flows out of the engine coolingcircuit into the low temperature circuit.
 20. The method as claimed inclaim 7, wherein warn coolant from the engine cooling circuit is usedfor the heating of charging air in the charging-air/coolant cooler.